1. Field of the Art
The disclosure relates generally to communication systems, and more specifically, to low power optical transmission.
2. Description of the Related Art
Worldwide demand for Internet bandwidth is growing rapidly each year, driven largely by video demand and the prevalence of mobile devices. 100 Gigabit Ethernet (100 GE) is quickly emerging in enterprise and datacenter environments, driving a need for 100 Gb/s router links between datacenters. As a result, service providers seek to deploy 100 Gb/s transmission technology on metro (40-1000 km) and long haul (>1000 km) optical networks.
Coherent transmission and direct detection represent two classes of modulation technologies that are commonly used for 100 G dense wavelength division multiplexing (DWDM) optical networks. In coherent transmission, the transmitter modulates both phase and amplitude of the optical carrier. In direct detection, the transmitter modulates only amplitude of the optical carrier while phase information is lost. Direct detection can be used for metro applications, but only with significant limitations using existing technology. For example, current 100 Gb/s direct detection systems utilize four wavelengths (each carrying 25 Gb/s data) instead of one as in coherent systems, utilize expensive optical dispersion compensation to achieve metro reaches, and are much more sensitive to impairments like chromatic dispersion, polarization mode dispersion, and optical amplifier noise than coherent systems. Coherent transmission is typically better suited for long haul networks, where maximizing fiber capacity is generally the most important feature. However, coherent networks are not traditionally used for metro applications due to the high cost and power consumption of traditional coherent transmission systems.